The authors tested the effect of cold water ingestion during high-intensity training in the morning vs the evening on both core temperature (T C) and thermal perceptions of internationally ranked long-distance swimmers during a training period in a tropical climate. Nine internationally ranked long-distance swimmers (5 men and 4 women) performed 4 randomized training sessions (2 in the evening and 2 in the morning) with 2 randomized beverages with different temperatures for 3 consecutive days. After a standardized warm-up of 1000 m, the subjects performed a standardized training session that consisted of 10 × 100 m (start every 1′20″) at a fixed velocity. The swimmers were then followed for the next 3000 m of the training schedule. Heart rate (HR) was continuously monitored during the 10 × 100 m, whereas T C , thermal comfort, and thermal sensation (TS) were measured before and after each 1000-m session. Before and after each 1000 m, the swimmers were asked to drink 190 mL of neutral (26.5 ± 2.5°C) or cold (1.3 ± 0.3°C) water packaged in standardized bottles. Results demonstrated that cold water ingestion induced a significant effect on T C , with a pronounced decrease in the evening, resulting in significantly lower mean T C and lower mean delta T C in evening cold (EC) than in evening neutral (EN), concomitant with significantly lower TS in EC than in EN and a significant effect on exercise HR. Moreover, although T C increased significantly with time in MN, MC, and EN, T C was stabilized during exercise in EC. To conclude, we demonstrate that a cold beverage had a significant effect on T C , TS, and HR during training in high-level swimmers in a tropical climate, especially during evening training.